1.1 What is the coefficient of restitution? (problem motivated)

every time a ball with a velocity hits something, it changes its velocity

now in science and engineeriing, we often want to predict the future and in order to predict the future, it would be useful to know what the velocity of our ball is after the ball hit something

visual: a black background with a white box

now in general we assume that the component

different objects colliding bump different much

it is basically a constraint, applied to the relative velocities of 2 colliding bodies